Red Cedar Trees Rebounded After Clean Air Act

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A species of old trees in the Appalachian Mountains is growing
faster than expected in the wake of clean-air controls
implemented decades ago, a new study shows.

The research on eastern red cedar trees — all between 120 and 500
years old — also showed changes in the types of carbon and sulfur
in their
tree rings a few years after the Clean Air
Act was enacted in 1970.

"The first thing that got us interested was how these old trees
are doing, and what are some of the physiological mechanisms that
allow the old trees to stay alive," Richard Thomas, a biology
researcher at the University of West Virginia, told LiveScience.

"When we saw all this change in growth and the change in isotopes
in the early 1980s, the research went into a different direction
... it was like a detective story, almost, trying to eliminate
each little thing."

The Clean Air Act requires the Environmental Protection Agency to
set air quality standards for six "criteria pollutants": carbon
monoxide, lead, nitrogen dioxide, ozone, sulfur dioxide and
particulate matter. It also has provisions to address problems
such as
acid rain.

Before its implementation, the Appalachians were a "bull's-eye"
for acid pollution due to a large number of power plants along
the Ohio Valley, Thomas said. The effects were clear in core
samples taken from the trees: sulfur isotopes (variations of an
element with a different number of neutrons) pointed to
pollution, and carbon isotopes showed that the trees' stomata
(the pores that are opened and closed to regulate the exchange of
carbon dioxide and water) were closing.

But a decade after the Clean Air Act was implemented, the stomata
began to open and, slowly, they continued to do so until the
early 2000s. Photosynthesis and the growth of the trees also
accelerated. Meanwhile, sulfur isotopes in the wood of tree rings
approached levels not seen since the preindustrial age.

Results from the 1930s, the Great Depression era, were almost
identical to the results from post-1980, Thomas said. The
suppressed economy during the Great Depression led to
reduced fossil fuel emissions. Tree rings from the 1930s
showed improved tree growth and physiology.

Thomas and his team now aim to broaden their search to more
species of trees and a wider geographic area.

The study was detailed in the Sept. 2 issue of the journal
Proceedings of the National Academy of Sciences.